Traditional mailing lists (such as ones created by a vanilla install of GNU Mailman) do not work they way you describe.
They work like this:
1. You send a message to a mailing list address. This address belongs to a software agent which sends the message to everyone. Your From: header is clearly preserved. The mailing list robot adds itself to the Cc: line to stay in the loop.
2. Someone who wants to continue your discussion publicly hits Reply All. At this point, the mail software composes a a new message which To: you, From: this person, and Cc: to the mailing list.
3. You receive the message directly. The robot also receives it because it is in the Cc: loop, and sends it to the subscribers. (If you're also one of the subscrbers, and the list is configured that way, it will avoid sending you a "list copy").
4. And so it goes.
But what do I know; I have only used mailing lists for 25 years, and run mailing lists of my own on my own server.